Barometer preheater



Nov. 11, 1952 c. G. DAHM ET AL 2,617,305

BAROMETER PREHEATER Filed Dec. 16, 1947 2 SHEETSSHEET 1 wamw A TTORNEYTia- Nov. 11, 1952 c. e. DAHM ETAL BAROMETER PREHEATER 2 SHEETS-SHEET 2Filed Dec. 16, 1947 ATTORNEY Patented Nov. ll, 1952 UNITED STATES PATENTOFFICE BAROMETER PREHEATER Application December 16, 1947, Serial N 0.791,978

7 Claims.

This invention relates to barometric measuring instruments and moreparticularly to a barometer disposed within a constant-temperatureenclosure and has for an object the provision of paths for flow of airto and from the atmosphere and barometer by means of which paths the airflowing therethroough is heated to the temperature of the barometer.

This invention is particularly applicable to barometric measuringsystems or instruments of the type disclosed in copending application,Serial No. 655,660, filed by George E. Conover, a coworker of ours. Insuch a system flow-connections are provided between the barometer andthe atmosphere in order for the barometer to indioate changes inbarometric pressure. Upon the occurrence of such changes there is a flowof air to or from the barometer. The barometer itself is disposed withina chamber, the temperature of which is maintained well above the ambienttemperature, or the temperature of the air. Accordingly, air flowing tothe barometer is of lower temperature than that maintained in theconstant-temperature enclosure and produces temperature variationswithin the barometer. For accurate readings it was found necessary towait long periods of time, in some instances as long as forty (40)hours, for constant temperature conditions to be restored. The flow ofair to barometers of the foregoing type is caused by the use of bellowswhich changes the volume and pressure within a chamber. Ingress ofcooler air to the bellows produces dimensional changes therein whichadversely affect the reading of the barometer.

It is an object of this invention to avoid delays in obtaining accuratereadings of barometric pressure by eliminating the effects oftemperature variations of the atmoshere on the barometer. Morespecifically, there are provided means for assuring that all airentering the barometer will be at a constant temperature. This, in oneform of the invention, is accomplished by providing between thebarometer and atmosphere heat transfer paths, which paths are maintainedat a constant temperature and thus heat the air as it passestherethrough to the temperature of the barometer. By this means, thebarometer as a whole is temperature-stabilized.

For further objects and advantages of the invention, reference should behad to the following description, taken in conjunction with theaccompanying drawings, in which:

Fig. 1 diagrammatically illustrates the invention and the principalparts of a barometer to which the invention is particularly applicable;

Fig. 2 is a cross-sectional view of a barometric instrument embodyingthe invention, taken along line Z2 of Fig. 3;

Fig. 3 .is a plan view of the instrument of Fig. 2; and

Fig. 4 is a sectional view taken along line 4-4 of Fig. 2 with certainparts omitted.

Though the invention may be applied to other types of pressure measuringinstruments adversely affected by temperature variations and whereinoperating parts are preferably to be maintained at constant temperaturewithin a constant-temperature enclosure, it has been illustrated asapplied to a barometer of such sensitivity as to be highly useful inmeasuring differences in elevations.

In order more fully to understand the utility of the invention, theoperation of the barometer itself will first be explained. Referring nowto Figs. 1 and 2 the barometer comprises a normally sealed chamber [0and a normally unsealed chamber H connected by a capillary tube 13. Thevolume of chamber I 0 may be varied by means of flexible bellows M. Thebellows I4 is expanded or contracted by knob [5 which drives shaft [6threaded in a support IT. The chamber l0 may be opened to the atmospherethrough an elongated tube 2|] under the control of valve 21. Thecapillary tube I3 includes the two inverted U-sections, 22 and 23respectively, forming traps for a small quantity of liquid, which willbe referred to as bubble 24 which is placed in a horizontal section ofthe tubing located between the traps 22 and 23. The valve 25 is disposedbetween the liquid trap 23 and the normally unsealed chamber II. Thenormally unsealed chamber I l is connected to the atmosphere by anelongated tube 26 under the control of valve 21.

At a first or a base station generally of a known elevation, valve 25 isclosed by rotation of knob 25-A, and the null position of bubble 24 isaccurately determined with the aid of viewing eye- :piece 28, Fig. 3.Valves 2! and 2'! are opened by rotating knobs 2l-A and 2l-A, the knobI5 is then rotated to a predetermined position thereafter taken as itsreference position, and the position of the bubble 24 with respect tothe scale 29 is thereafter taken as its null position. The valve 2| isthen closed and remains closed until a new base station has been reachedor is to be established.

The valve 2'! is now closed preparatory to transport the barometer to asecond location or sta- 3 tion. With the instrument at said secondstation or location the valve 25 is opened, and the valve 21 ismomentarily opened by depressing knob 2l-B which controls a very smallorifice of valve 21. If a difference of atmospheric pressure existsbetween the two stations, the resultant pressure differential betweenchamber In and chamber II will cause bubble 24 to move and to seek anequilibrium position. The volume of, and pressure within chamber ID isthen changed by turning knob in the direction which returns bubble 24 toits original or null position. By successive steps of momentarilyopening the small orifice of valve 21 and adjusting knob IS, thepressure in chamber ID will be made to equal the atmospheric pressureand the knob 2'I-A may be rotated to open a relatively large orifice ofvalve 2'! which may be left open with bubble 24 remaining in the nullposition. The position of pointer 58 with respect to its cooperatingscale I!) is then noted and the difference between the readings ofpointer l8 on scale l9 (or in Figs. 2, 3 and 4 the readings of counterl9-A for the two locations or stations) is a measure of the diiferencein atmospheric pressure between the two points and thus the differencein elevation between them may be determined. The difference in elevationbetween the base station and any further stations may be similarlydetermined as will be the practice in making elevation surveys.Obviously, diiference in elevations between any selected stations may bereadily determined.

For further description of these and other features of such a barometricmeasuring instrument as above briefly described, reference should be hadto the above identified copending application Serial No. 655,660.

It will be remembered that upon a change in atmospheric pressure, airwill, upon opening of valve 21, flow to or from chamber I l If air flowsinto chamber l I, a change in temperature will occur because chamber IIis maintained above the the ambient temperature. To avoid the effect oftemperature changes and to eliminate errors arising therefrom, theforegoing Conover application disclosed the disposition of chamber i E]within an outer chamber H. The unit thus constructed, Fig. 2, isdisposed within a normally unsealed constant-temperature chamber 35.Even though the chamber 35 was maintained at constant temperature abovethe ambient, for example, at 150 F., as by thermostatically controlledheater elements 36, the ingress of cooler air to chamber l I gave riseto errors unless readings were taken only after constant-temperatureconditions prevailed, a matter which required long waitin periods.

In avoidance of the foregoing problem and in accordance with the presentinvention, the air flowing to chamber H is preheated to the establishedtemperature. A preheater in the form of elongated tubing 26 is disposedwithin the chamber 35 and air flows from valve 21 by way of preheatercoil 26 to the chamber H. Due to the heat transfer which takes place theair is heated to the constant temperature, as 150 F., and its entry intochamber ll causes no temperature changes therein.

A further difliculty in operation of the barometer of the aforesaidConover application arose during the establishment of a new base stationand in the taking of readings or measurement of elevation at other knownbase stations. For example, in operation of the instrument to establisha new base station or to take a new base 4 reading, the bubble 24 ismoved to its null position by knob l5, the valve 25 is closed and thevalves 2| and 2'! are opened, which allows air to flow into or out ofchamber ll through the tube 26 as explained above, and to or from thechamber l0 and chamber 35.

The temperature in chamber 35 is maintained essentially constant butsince it is not a sealed chamber, rather one open to the atmosphere, thetemperature of the air in that chamber may and usually does differsomewhat from the established temperature in chambers l0 and H. Thepresent invention provides that air flowing from chamber 35 into chamberIn will be heated to the established temperature of the chamber l0 andwill cause no change of temperature therein. Thus, a preheater in theform of tube 20, similar to tube 26, is disposed within chamber 35 andconnected to chamber l0 through the Y-connection 26-A and valve 2|. Heattransfer between tube 29 and air flowing from chamber 35 to chamber IDwill cause any air entering chamber 10 to be at the establishedtemperature.

The invention further provides that air entering the bellows l4 when thevolume of the bellows is increased will also be at the establishedtemperature. To assure that the air entering bellows i4 is thusconditioned, the Y-connection til-A is utilized to afiord entry of airfrom the tube 20 into the bellows M.

The invention thus provides paths through which air entering eitherchamber ID or H or the bellows I4 is conditions to eliminate instabilityof the instrument inherent when the ingressive air is cooler than thechambers ID or H or the bellows 14 that it enters.

The invention thus applied completely temperature-stabilizes thebarometer making possible continuous surveyin operations, the accuracyof which is unaffected by pressure differences which result in ingressor egress of air to or from the barometer.

Each of the preheater coils in the above illustration was formed fromone-eighth inch copper tubing having a one-sixteenth inch (1%") insidediameter, and a length of two feet (2'). They are preferably metallic,but may be nonmetallic, as of glass, and may have dimensions dictated bythe particular application. The volume of each of the preheaters inapplications of this invention depends upon the operating range andconditions under which the instrument is operated. That volume ispreferably equal to or greater than the volumetric change of air due tooperation of the instrument from one extreme of its range to the other.More particularly, the volume of each of preheaters 20 and 26 may beequal to the change in the volume of the bellows I4 when knob I5 isrotated from one limit to the other. Thus air moved from the preheaters2G and 26 will always be at the same temperature. In some applications,however, the preheaters may be of smaller volume as dictated by therelationship between efficiency of heat transfer and the range ofvariations of pressure to be measured. So long as a time-temperaturerelation is maintained with reference to the rate of heat transfer as toinsure constancy of the temperature of the air or fluid flowing into theinstrument, the requirements of the present invention are met. In otherwords, the length of the heat-transfer path has that relation to therate or volume of fluid flow which produces constant-temperature fluidin the instrument. Where the chambers I 0 and H are large, obviously agreater timetemperature factor will be required. In the specificapplication of the invention already referred to this requirement hasbeen met by providing the one-eighth inch /8") tubing, two feet (2')long, the volume of which is greater than the volume of air movedtherethrough upon operation of the instrument from one limit to theother.

Although a preferred embodiment and a particular application of thepresent invention has been described, it is to be understood thatfurther modifications may be made within the scope of the appendedclaims.

What is claimed is:

1. In a barometric measuring system, means for avoiding the alterationof the reading of the barometer due to flow of air thereto of adifferent temperature than that of the barometer comprising aconstant-temperature chamber having said barometric measuring meansdisposed therein, heating means for the air in said chamber, a structuredisposed in heat-transfer relation with the heated air of said chamberand which provides a sinuous path for flow of atmospheric air to saidbarometric measuring means at the same temperature as said chamber, andvalve means for opening said structure to atmosphere for displacement ofair from said structure to and from said barometer.

2. A barometric measuring system of the type in which a barometer havingtwo chambers connected by a null indicating means is disposed within,and maintained at the temperature of, a constant-temperature chamber,characterized by the provision of heating means for said chamher andmeans for avoiding alteration of the reading of the barometer whichwould arise by flow of atmospheric air thereto at a differenttemperature than that of the barometer comprising conduit means formingelongated paths for the flow of air from the atmosphere to thebarometer, said conduit means being disposed to be heated to the sametemperature as said chamber for delivery of air at the same temperatureas said barometer, and valve means opening said conduit to theatmosphere for displacement of air from said conduit means to and fromsaid barometer.

3. Means for stabilizing a pressure measuring instrument disposed in aconstant-temperature chamber comprising a preheater having a flowpathdisposed in heat-transfer relation with said constant-temperaturechamber and fluidconnected to the pressure measuring instrument, heatingmeans for said chamber, said flow-path having a length in relation torate of fluid-flow which brings to the temperature of said chamber allfluid passing therethrough to said instrument, and valve means openingsaid flow-path to atmosphere for displacement of air therein to and fromsaid pressure-measuring instrument.

4. In a pressure measuring instrument wherein two chambers are disposedwithin a constanttemperature enclosure and interconnected by indicatingmeans responsive to pressure differences between the two chambers, anddisplaceable means within one of said chambers for varying the volumethereof, the combination of preheaters associated with each of saidchambers, each comprising a coil of tubing disposed within saidconstant-temperature enclosure, and each of said coils having one endopen to the atmosphere and the other end to its respective chamber.

5. In a pressure measuring instrument wherein two chambers are disposedwithin a constanttemperature enclosure and interconnected by indicatinmeans responsive to pressure difierences between the two chambers, anddisplaceable means within one of said chambers for varying the volumethereof, the combination of means including a heater for holdin constantthe temperature of said enclosure, preheaters associated with each ofsaid chambers and each comprising a coil of tubing disposed within, andmaintained at the same temperature as that of, said constanttemperatureenclosure, and each of said coils having one end open to the atmosphereand the other end to its respective chamber, the volume of each of saidpreheaters being at least equal to the maximum change of volume of oneof said chambers by the operation of said displaceable meanstherein fortransfer of air to and from each of said chambers without change of thetemperature of the air within said chambers.

6. In a pressure measuring instrument wherein a constant-volume chamberand a variablevolume chamber are disposed in a constanttemperatureenclosure and interconnected by indicating means responsive to pressuredifferences between the two chambers, the combination of means includinga heater for holding constant the temperature of said enclosure, apreheater which comprises tubing disposed within, and maintained at thesame temperature as that of, said constant-temperature enclosure,controlling means associated with said tubing, one end thereof beinconnected to said constant-volume chamber, and the other end thereofbeing open to atmosphere for flow of air in either directiontherethrough for transfer of air to and from each of said chamberswithout change of the temperature of the air within said chambers.

'7. In a pressure measuring instrument where- 'in two chambers aredisposed within a constanttemperature enclosure and interconnected byindicating means responsive to pressure differences between the twochambers and displaceable means within one of said chambers for varyingthe volume thereof, the combination of means including a heater forholding constant the temperature of said enclosure, preheatersassociated with each of said chambers and with said volume varyingmeans, each preheater comprising a coil of tubing disposed within andmaintained at the same temperature as that of said constanttemperatureenclosure and flow-controlling means associated with each of said coilscontrolling flow of air in either direction therethrough for transfer ofair to and from each of said chambers without change of the temperatureof the air within said chambers.

CORNELIUS G. DAHM. DAYTON H. CLEWELL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,805,321 Ullman May 12, 19311,908,042 Moore May 9, 1933 2,339,229 Wyllie Jan. 11, 1944 2,434,837Cornett Jan. 20, 1948 FOREIGN PATENTS Number Country Date 28.625 GreatBritain "My. Dec, 1 191a

